PROJECTSUMMARY/ABSTRACT Theoverallgoalofthisproposalistoprovidekeyinsightsintotheexcessaccumulationof smoothmusclecells(SMCs)thatcharacterizesmultiplevascularpathologies.TheGreiflabandother groupshaveshownthatpathologicalremodelinginducedinatherosclerosisorhypoxiainvolvesrobust clonalexpansionofrareSMCprogenitors.Herein,weproposetostudythemacrophage-mediated regulationofSMCprogenitorsinvasculardisease.Werecentlyidentifiedapoolofsmoothmuscle progenitorsthatwehavetermed?primed?cells(asinprimedtomuscularize),locatedateach muscular-unmusculararterioleborderinthelungandwithauniquemolecularsignatureexpressing SMCmarkersandtheundifferentiatedmesenchymemarkerplatelet-derivedgrowthfactorreceptor (PDGFR)-?.Withhypoxiaexposure,oneoftheseprogenitorsclonallyexpandsgivingrisetothevast majorityofSMCsthatcoatthenormallyunmuscularizeddistalarteriole.Macrophagesaccumulatein thelungwithhypoxiabuttheirroleintheensuingvascularremodelingisnotwellunderstand.Our initialstudiesdemonstratethatmacrophagesinthehypoxiclunghaveenhancedlevelsofhypoxia- induciblefactor(HIF)-?andtheligandplatelet-derivedgrowthfactor(PDGF)-B.Furthermore,we demonstratethatdeletionofPdgfbwithtwoindependentknock-inmice(LysM-CreorCsf1r-CreER), whichinducerecombinationinmacrophages/monocytes,attenuateshypoxia-induceddistalarteriole muscularization.Additionally,macrophagedepletioninhibitspathologicalvascularremodeling.We hypothesizethatlungmacrophageHIF-?isrequiredcellautonomouslyforhypoxia-inducedPDGF-B expression,andmacrophage-derivedPDGF-BiscriticalforprimedSMCproliferationand dedifferentiationinpulmonaryvascularremodeling.Totestthishypothesis,wewillutilizetransgenic mice,primedcellsandmacrophagesubpopulationsisolatedfromthemouselungaswellashuman monocytesandpulmonaryarterySMCs.Wehavecarefullyassembledagroupoftop-notch collaboratorswithdiverseexpertise,rangingfrommacrophagesinvascularandlungdiseasesto bioengineeringofnanoparticles,whichwillfacilitatebringingtheproposaltofruition.Thisproposal specificallyaimsto:1)elucidatecellularmechanismsunderlyingmacrophage-derivedPDGF-B inductionofdistalpulmonaryarteriolemuscularizationinhypoxia;?2)assessroleofspecific macrophagepopulationsinhypoxia/PDGFB-inducedpulmonaryvascularremodeling;?and3) determinetheroleofmacrophageHIF-?inhypoxia-inducedPDGF-BexpressionandinPDGF-B- mediateddistalmuscularization.Insum,theproposedstudieswillyieldfundamentalinsightsintothe roleofmacrophage-SMCprogenitorinteractionsinvasculardiseaseandtherebysuggestnovel therapeuticstrategies.